PHP 中文字符串截取

/**
 *
 * 中文字符串截取
 * @param string $string
 * @param int $sublen
 * @param int $start
 * @param string $code
 */
function substr_zh($string, $sublen, $start = 0, $code = 'UTF-8') {
    if ($code == 'UTF-8') {
        $pa = "/[\x01-\x7f]|[\xc2-\xdf][\x80-\xbf]|\xe0[\xa0-\xbf][\x80-\xbf]|[\xe1-\xef][\x80-\xbf][\x80-\xbf]|\xf0[\x90-\xbf][\x80-\xbf][\x80-\xbf]|[\xf1-\xf7][\x80-\xbf][\x80-\xbf][\x80-\xbf]/";
        preg_match_all( $pa, $string, $t_string );

        if (count( $t_string[0] ) - $start > $sublen) return join( '', array_slice( $t_string[0], $start, $sublen ) ) . "...";
        return join( '', array_slice( $t_string[0], $start, $sublen ) );
    } else {
        $start = $start * 2;
        $sublen = $sublen * 2;
        $strlen = strlen( $string );
        $tmpstr = '';

        for($i = 0; $i < $strlen; $i ++) {
            if ($i >= $start && $i < ($start + $sublen)) {
                if (ord( substr( $string, $i, 1 ) ) > 129) {
                    $tmpstr .= substr( $string, $i, 2 );
                } else {
                    $tmpstr .= substr( $string, $i, 1 );
                }
            }
            if (ord( substr( $string, $i, 1 ) ) > 129) $i ++;
        }
        if (strlen( $tmpstr ) < $strlen) $tmpstr .= "...";
        return $tmpstr;
    }
}